A sharpening apparatus for forage harvester cutterhead knives is disclosed in McClure et al U.S. Pat. No. 4,834,303. McClure et al discloses a forage harvester with a rotating cutterhead and an automatic grinding mechanism for sharpening the knives of the cutterhead. The grinding mechanism comprises a carriage carrying a grinding stone which is reciprocated back and forth across the cutterhead while the cutterhead is rotating. A shearbar is used in conjunction with the cutterhead.
Weaver, Jr. et al U.S. Pat. No. 4,799,625 discloses a method and apparatus for adjusting a shearbar relative to a cutterhead. It has been found that the sharpening apparatus of McClure et al produces a barrel-shaped cutterhead profile over a period of time, which profile has been found incompatible with the shearbar adjusting apparatus of Weaver, Jr. et al. The apparatus of Weaver, Jr. et al depends on contacting the two opposite corners of the rotating cutterhead to make the proper adjustment on the shearbar relative to the cutterhead profile. With a barrel-shaped cutterhead profile, it has been found that the apparatus of Weaver, Jr. et al is contacting one corner and an intermediate portion of the cutterhead, instead of the opposite corner. The effect is that the shearbar, instead of being adjusted parallel and close to the cutterhead, is adjusted at an angle to the cutterhead, producing a gap along a substantial portion of the shearbar relative to the cutterhead. This gap is undesirable, since it causes the crop material being harvested to be torn and shredded, requiring greater power and reducing the efficiency of the machinery.